In 1990, Bobby Kotick bought 25 percent of failing videogame maker Activision for $440,000, with financing from his mentor, casino king Steve Wynn. Since then, the company has been in nonstop-growth mode, through both internal expansion and acquisitions, and late last year, Kotick engineered his biggest deal yet—a nearly $19 billion merger with Vivendi’s game division. The prize for Activision: Blizzard Entertainment, maker of the online game World of Warcraft, which has about 10 million paying subscribers. Vivendi will own a majority stake in the merged company, to be renamed Activision Blizzard, and Kotick will run it.